1. Field of the Invention
The present invention relates to an illuminator used for image processing measuring instrument and other optical measuring instrument for measuring dimension and profile of a workpiece based on an image of the workpiece obtained through an optical system. More specifically, it relates to an improvement of an illuminator for irradiating illumination light to the workpiece from a direction slanting relative to an optical axis of the optical system.
2. Description of Related Art
In an image processing measuring instrument for optically magnifying a target portion of a workpiece by a magnifying optical system to measure a dimension and profile of the workpiece based on the magnified image, such as a tool maker""s microscope, a projector and a visual-type coordinates measuring machine, illumination to the workpiece plays an important role for obtaining the magnified image of the workpiece.
Conventionally, a vertical downward illumination method, in which the illumination light is irradiated onto the workpiece approximately from right above, has been known as an illumination method of the image processing measuring instrument. However, the vertical downward illumination method is often used for measuring a workpiece having relatively simple profile, and is not suitable for measuring a workpiece having complicated profile such as a step-shaped workpiece having a large number of edge portion, where shadow of the edge portion is sometimes blurred on the display.
To solve the above disadvantage, following illuminators have been proposed for clearly detecting the shadow of the edge portion by irradiating the illumination light onto the workpiece in a direction slanting at a predetermined angle relative to an optical axis of the magnifying optical system.
Conventional example 1 has a fiber illuminator for irradiating the illumination light parallel to the above-described optical axis of the optical system, a parabolic mirror for reflecting the illumination light from the fiber illuminator in a direction approximately orthogonal with the optical axis of the optical system and a ring mirror for condensing the illumination light reflected by the mirror onto the workpiece.
In the conventional example 1, illumination angle relative to the target portion is changed by adjusting advancement and retraction of the parabolic mirror relative to the illuminator and relative position of the ring mirror on the optical axis.
Conventional example 2 has the same fiber illuminator, a ring-shaped condenser lens for refracting the illumination light to be away from the optical axis of the optical system, and a ring-shaped reflecting member for condensing the illumination light refracted by the condenser lens (Japanese Utility Model Laid-Open Publication No. Hei 7-23208).
The conventional example 2 has a plurality of petal-like mirror piece disposed on a circle around a center of the optical axis with a part thereof being sequentially overlaid, an end of the mirror piece opening and closing to change the illumination angle of the workpiece.
Conventional example 3 has a plurality of LED directed to the workpiece around the optical axis for irradiating the light, lighting position of the LED being controlled to change the illumination angle.
Conventional example 4 has a ring-shaped lens around the optical system and the angle of the light irradiated onto the workpiece is adjusted by moving the light source in radial direction of the lens above the ring-shaped lens.
Conventional example 5 uses a peripheral portion of an objective remote from the optical axis of the objective for obliquely irradiating the illumination light onto the workpiece (Japanese Patent Laid-Open Publication No. Hei 8-166514).
Conventional example 6 has a reflection mirror for reflecting the illuminating light irradiated from the light source, and a stationary fresnel lens for condensing the illumination light reflected by the mirror to the workpiece.
However, following problems occurs in the above conventional examples.
In the conventional example 1, the reflection surface of respective mirrors has to be formed to have parabolic cross section for obtaining predetermined reflection light from the fiber illuminator with the use of two pairs of mirror, which requires high-leveled surface processing, thus increasing production cost. Further, complicated moving mechanism is required for relatively moving the mirrors, thereby also increasing production cost.
Since the conventional example 2 has a complicated structure of the plurality of the petal-like mirror piece, and the ring-shaped reflecting member is opened and closed by synchronously moving all the mirror pieces, adjustment of the illumination light onto the workpiece is difficult.
In the conventional example 4, since the size of the ring-shaped lens increases in order for obtaining large illumination angle, there is limitation in changing the illumination angle. Further, the illumination angle cannot be changed when a ring-shaped fiber illuminator is used as the light source. Accordingly, linear fiber illuminator has to be used, which can cause illumination uniformity in measuring a cylindrical workpiece.
Since the illumination angle of the conventional example 5 is determined in accordance with diameter of the objective etc., the illumination angle cannot be changed.
In conventional example 6, since the fresnel lens is fixed, the illumination angle cannot be changed as in the conventional example 5.
An object of the present invention is to solve the above conventional problems and to provide an illuminator for optical measuring instrument having a simple configuration and being capable of easily changing illumination angle toward the workpiece.
For achieving the object, the present invention refracts the illumination light from a light generator by a condenser lens to be condensed onto the optical axis and changes the illumination angle by moving the condenser lens along the optical axis.
Specifically, an illuminator for optical measuring instrument according to the present invention has: a light generator for generating illumination light radially from a center of an optical axis of an optical system toward outside; and an illumination angle adjuster for condensing the illumination light from the light generator toward a workpiece, the illumination angle adjuster having a condenser lens for refracting the illumination light from the light generator and being movable along the optical axis.
According to thus arranged present invention, the illumination light generated by the light generator is irradiated onto the workpiece by the condenser lens constituting the illumination angle adjuster. In order to change the illumination angle of the illumination light to the workpiece, the condenser lens is moved along the optical axis. For instance, for narrowing the illumination angle of the illumination light irradiated onto the workpiece, the condenser lens is put on a position adjacent to the light generator. Then, the illumination light generated by the light generator is refracted by an inner side portion of the condenser lens to be irradiated on the workpiece at a small angle.
On the other hand, for enlarging the illumination angle, the condenser lens is put on a position remote from the light generator. Then, the illumination light generated by the light generator is refracted by a peripheral portion of the condenser lens to be irradiated onto the workpiece at a large angle.
Accordingly, the illumination angle of the illumination light can be easily changed by arranging the illumination angle adjuster with a simple structure of the condenser lens and by moving the condenser lens along the optical axis.
In the above arrangement, the condenser lens may preferably be an annular lens disposed coaxially with the optical axis of the optical system.
Accordingly, the illumination light reflected by the workpiece can be observed by the optical system through the optical axis of the optical system without being blocked by the annular lens, thus achieving proper measurement.
The condenser lens may be arranged in plural.
Accordingly, the illumination angle to the workpiece can be fine adjusted by placing the condenser lenses along the optical axis and by adjusting relative distance thereof.
The light generator may have a fiber illuminator formed in a ring-shape with the optical axis as a center thereof or a LED illuminator formed in a ring-shape with the optical axis as a center thereof.
According to the above arrangement, light volume and/or irradiation position can be easily changed by selectively switching on and off the fiber illuminator or the LED illuminator.